Standard 802.1Q promulgated by the Institute of Electrical and Electronics Engineers (Std. 802.1Q) entitled “Virtual Bridged Local Area Networks” defines a convention for supporting, among other things, traffic prioritization in bridged local area networks (LANs). The Std. 802.1Q priority is signaled through the network. That is, a tag which may include, among other things, a virtual LAN (VLAN) identifier and a priority, is transmitted in the packet through the network and applied at bridges to prioritize the packet. Generally speaking, the VLAN identifier determines where the packet may be transmitted and the priority determines how fast the packet will be processed relative to other packets.
The Std. 802.1 Q convention also provides for tag priority “regeneration”. That is, each bridge receiving a Std. 802.1Q-complaint packet may regenerate the inbound tag priority and instantiate the regenerated tag priority in the packet prior to transmission. The regenerated tag priority is instantiated in lieu of the inbound tag priority, but may be the same value or a different value.
While Std. 802.1Q provides a useful convention for prioritizing traffic in a bridged network, it may be desirable to implement the convention on a selective basis. That is, on one or more bridges in the network, it may be desirable to prioritize a “tagged” packet based on a different priority convention or not at all. Or it may be desirable to prioritize certain tagged packets based on tag priority and to prioritize other packets based on a different convention or not at all. Even where a tagged packet is not prioritized based on tag priority, however, it may still be desirable to preserve Std. 802.1Q priority signaling, including tag priority regeneration and instantiation, for potential downstream application. Accordingly, there is a need for priority processing for a data communication switch, such as a LAN switch supporting Std. 802.1Q, which selectively prioritizes tagged packets based on a tag priority, such as that defined in Std. 802.1Q, but which preserves tag priority signaling for all tagged packets.